In the manufacturing of an IC product, a wafer is processed at many work stations or processing machines. The transporting or conveying of partially finished products, or work-in-process (WIP) parts, is an important aspect of the total manufacturing process. The conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit (IC) chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e. as many as several hundred, is required to complete the fabrication process. A semiconductor wafer or IC chips must be transported between various process stations in order to perform various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, ion implantation, etching and passivation steps must be carried out before a chip is packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e., a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically guided vehicles or by overhead transport vehicles that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes or SMIF pods and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rails of the conveying vehicle.
In an automatic material handling system (AMHS), stockers are widely used in conjunction with automatically guided or overhead transport vehicles, either on the ground or suspended on tracks, for the storing and transporting of semiconductor wafers in SMIF pods or in wafer cassettes. For instance, as shown in FIG. 1, three possible configurations for utilizing a stocker are illustrated. In case A, a stocker 10 is utilized for storing WIP wafers in SMIF pods and transporting them first to tool A, then to tool B, and finally to tool C for three separate processing steps to be conducted on the wafers. After the processing in tool C is completed, the SMIF pod is returned to stocker 10 for possible conveying to another stocker. The configuration shown in case A is theoretically workable but hardly ever possible in a fabrication environment since the tools or processing equipment cannot always be arranged nearby to accommodate the processing of wafers in stocker 10.
In the second configuration of case B shown in FIG. 1, stocker 12 and a plurality of buffer stations A, B and C are used to accommodate different processes to be conducted in tool A, tool B and tool C. As shown in FIG. 1, a SMIF pod may be first delivered to buffer station A from stocker 12 and waits there for processing in tool A. Buffer stations B and C are similarly utilized in connection with tools B and C. The buffer stations A, B and C therefore become holding stations for conducting processes on the wafers. This configuration provides a workable solution to the fabrication process, however, requires excessive floor space because of the additional buffer stations required. The configuration is therefore not feasible for use in a semiconductor fabrication facility.
In the third configuration shown as case C in FIG. 1, stocker 14 is provided for controlling the storage and conveying of WIP wafers to tools A, B and C. It is seen that after a SMIF pod is delivered to one of the three tools, the SMIF pod is always returned to stocker 14 before it is sent to the next processing tool. This is a viable process since only one stocker is required for handling three different processing tools and that no buffer station is needed. The configuration shown in case C illustrates that the frequency of use of the stocker is extremely high since the stocker itself is used as a buffer station for all three tools. The accessing of stocker 14 is therefore much more frequent than that required in the previous two configurations.
In modern semiconductor fabrication facilities, especially for the 200 mm or 300 mm FAB plants, automatic guided vehicles (AGV) and overhead transport vehicles (OHT) are extensively used to automate the wafer transport process as much as possible. The AGE and OHT utilize the input/output ports of a stocker to load or unload wafer lots, i.e., normally stored in SMIF pods.
An automatic guided vehicle (AGV) system used in a conventional stocker configuration is shown in FIG. 2. The AGV system 48 consists of two automatic guided vehicles 50 and 52 with vehicle 52 stopped in front of the stocker 30. The stocker 30 is equipped with an input port 54 and an output port 56. As shown in FIG. 2, the automatic guided vehicle 52 approaches the output port 56 for accepting an output from stocker 30, however, at the same time, the input port 54 is also blocked by vehicle 52 such that the second vehicle 50 must wait for input until vehicle 52 has moved out of the way.
During the transfer of a wafer cassette holder, i.e. the transfer of a SMIF pod into or out of an input port 54 or an output port 56 of a stocker 30, an I/O port paddle or platform (not shown) of conventionally design does not have any provision for fixing the SMIF pod in place and preventing the pod from slipping off the platform. It is therefore possible that the wafer cassette holder, or the SMIF pod may be damaged during such pod transfer process. Furthermore, there is no securing means on the paddle or platform, a clean room operator may mistakenly swap pods between paddles which leads to database inconsistency in an automatic material handling system (AMHS). It is therefore desirable to provide a securing means on a paddle or platform in a stocker to secure the position of a SMIF pod on the paddle for preventing damages to the pod, or preventing damages to the wafer stored therein, and for preventing database inconsistency in the AMHS.
It is therefore an object of the present invention to provide a platform for securely mounting a wafer cassette holder thereon that does not have the drawbacks or shortcomings of conventional platforms.
It is another object of the present invention to provide an I/O port paddle in a stocker for securely mounting a SMIF pod thereon without the possibility of damaging the pod or the wafers contained therein.
It is a further object of the present invention to provide a paddle for securely mounting a wafer cassette holder thereon by using securing means on the paddle surface for fixing the position of the wafer cassette holder.
It is another further object of the present invention to provide a platform for securely mounting a wafer cassette holder thereon by incorporating a securing means on a top surface of the platform juxtaposed to each of the four sidewalls of the wafer cassette holder.
It is still another object of the present invention to provide a platform for securely mounting a wafer cassette holder thereon by utilizing a securing means of engagement pins that are mounted on each side of the top surface of the platform.
It is yet another object of the present invention to provide a platform for securely mounting a wafer cassette holder thereon by utilizing a securing means of side panels mounted on each side of the top surface of the platform.
It is still another further object of the present invention to provide a method for preventing a wafer cassette holder from slipping off a cassette holder platform by utilizing securing means on the surface of the platform.
It is yet another further object of the present invention to provide a method for preventing a wafer cassette holder from being accidentally moved from a wafer cassette holder platform by engaging securing means to fix the position of the holder on the platform.